The present invention relates in general to railroad track switch heaters and, in particular, to impedance based and other heating systems that provide the desired heating for switches and other railroad components with reduced heating structure that can become damaged or pose hazards in the vicinity of a switch.
Railroad track switches typically involve a pair of stationary rails and a pair of switching rails that move between engaged and disengaged positions. In the engaged position, commonly referred to as the xe2x80x9creverse position,xe2x80x9d a switching rail abuts the gauge side of a stationary rail, i.e., the side which engages the flange of a train wheel, so as to divert the train wheel from the stationary rail and the corresponding track to another track. In the disengaged position, commonly known as the xe2x80x9cnormal position,xe2x80x9d the switching rail is separated from the gauge side of the stationary rail so that a passing wheel is unaffected by the switching rail.
In order to ensure proper functioning of a railroad switch, it is important that the switching rail and stationary rail make good contact in the engaged position. Accordingly, in cold climates, it is common to heat the rail switch or otherwise guard against build up of ice or snow at the switch, especially at the interface between the gauge side of the stationary rail and opposite side of the switching rail.
It will be appreciated that a malfunctioning switch presents a danger of derailment resulting in severe personal and property damage. Although switches are now normally equipped with sensors to provide advance warning in the event of a potentially malfunctioning switch, switch contact problems are nonetheless a hazard, can result in considerable delay and annoyance, and are a significant burden to the rail transportation system in cold climates. Switch malfunctions also result in loss of track time for cargo and other commerce, thereby adversely affecting profitability.
A number of different types of track switch heaters have been devised including heaters that operate on radiant (e.g., infrared element), convective (e.g., forced air); and/or conductive (e.g., electrical heater element) principles. Among these, certain heaters have relative advantages for particular applications based on efficiency, availability of an appropriate power source at a remote location or other considerations.
However, known track switch heaters are subject to one or more of the following disadvantages. First, some heaters can be damaged or can become worn due to repeated movement of the tracks incident to switching. In addition, some heaters are inefficient due to their reliance on convective or radiant heating. Other heaters are inefficient due to use of a small surface area for conductive heat transfer or uneven heat distribution across the heat transfer surface. In this regard, rounded heater element housings have a limited area of direct thermal contact and, in operation, such contact may be further limited if the housing becomes disfigured due to thermal warping or impact.
The present invention is directed to various implementations of a railroad track switch heating system that reduce or eliminate the need for heater elements or other heater components protruding from rail surfaces in the area of the switch. It has been recognized that such protruding elements are a common source of failures or malfunctions of heating systems. In particular, as noted above, the track switch environment is a rugged environment where protruding elements may be damaged by operation of the switch. In addition, such elements may be damaged during servicing of the track. For example, the track bed may be serviced periodically by machinery that grips and lifts the track or ties so that the bedding material can be restored. Such equipment can damage protruding elements. Moreover, the track itself may occasionally be manipulated by servicemen installing or repairing components related to track signaling and the like. Again, protruding elements are subject to inadvertent damage during such servicing. Protruding elements may also become warped, bent, or otherwise fail to maintain good thermal contact with the track, resulting in heating inefficiencies. In this regard, track surfaces may include raised lettering and other topological features that can interfere with good thermal contact between a rail and an external heating element. Such problems are reduced or eliminated by the present invention.
In accordance with the present invention, a heating system for heating a section of railroad track is disclosed. The heating system includes a power source for providing electrical power, a first heater assembly associated with a railroad structure located in the section of railroad track that is to be heated, wherein the heater assembly has at least a first heater structure which does not substantially protrude above the surface of the railroad structure; an electrical interface for applying an electrical potential across the heater structure in order to produce a current within the structure and control means to control the heat applied to the section of railroad track. Depending on the application, the power source may be, for example, a line of a power grid, where available, or a generator system, regardless of the source, the electrical power may be provided via either alternating current (AC) or direct current (DC) for use in the heating system. The control may include a processor for controllably delivering electricity to the electrical interface (e.g., via electrical leads) and a transformer to provide an electric signal suitable for heating the track without creating undue hazards for workmen or others. The controller may be associated with a thermal sensor to provide feedback regarding the temperature of the track. Feedback may also be provided regarding ambient conditions so as to provide an indication of potential ice buildup in the vicinity of the switch.
In a first aspect of the present invention the system""s heater assembly has a heater structure at least partially embedded within a railroad structure located in the section of the railroad track to be heated. In this regard, the heater structure may comprise some sort of separate heating element that is embedded within a railroad structure located in the section of railroad to be heated. Again, this embedded heating element will be substantially non-protruding above the surface of the railroad structure in which it is embedded.
Various refinements exist to the elements included in the first aspect of the present invention. For example, in one embodiment of the first aspect of the present invention, the heater structure is embedded in a railroad tie for placement beneath and interconnection with the track rails of the railroad section to be heated. The embedded heater structure is used to provide thermal energy to the track rails and the general area surrounding the track rails to clear snow and ice while not substantially protruding above the surface of the railroad tie. In many cases, concrete, metal or other prefabricated railroad ties are being used in place of traditional ties formed from timbers. The construction process for such ties (as well as conventional timber ties) can readily be adapted so that a heater structure may be embedded in a surface of these ties (e.g., an upper surface of the tie adjacent to the rail track attachment locations). Such heater structures may extend across the width of the tie or be exposed only in the area of the track rail. Preferably, the heater structure is embedded so that it is substantially flush with an upper surface of the tie. In this regard, one surface of the heater structure may be exposed on the tie""s surface such that the heater is disposed between the tie and the track rail upon assembly to increase heat transfer therebetween.
In another embodiment of the first aspect of the present invention, the heater assembly is embedded or interconnected with the track rail such that the heater structure does not substantially protrude above the surface of that track rail. In this regard, a recess may be formed on a surface or a void created within the cross-section of the rail structure that substantially conforms to the dimensions of a heater structure (e.g., a resistive heating element). As will be appreciated, utilizing a recess or void in the track rail surface provides for increased surface area contact between the track rail and a heating structure (e.g., three sides of a rectangular heating element) in addition to protecting the heater structure from the harsh railroad environment. This recess may be formed on the track rail""s web or, more preferably, on the track rail""s bottom surface such that the heater structure is further isolated from the rail environment, thus providing a system having increased reliability. Where the rail section is formed with an internal cavity for receiving the heater structure, it will be appreciated that there is substantially no convective and/or radiative heat transfer losses from the heater element to the atmosphere, thus providing a highly efficient track rail heating system.
In either of the above embodiments of the first aspect of the present invention, the embedded heater structure may comprise a resistive type heater element that may comprise one or more separate pieces. For example, the heater structure may comprise a sleeve member embedded with the railroad structure (i.e., tie, track rail, etc.) and an electric resistive heater element slidably receivable within the sleeve member. Preferably, the sleeve is attached to the railroad structure such that the slidably receivable heater element may be readily inserted and removed from the sleeve member, thus, providing for a heating system that is easily maintainable. Alternatively, this sleeve may be directly heated using an impedance heating system as discussed below. Additionally, a cartridge heater such as a split sheath cartridge heater. may be inserted into the sleeve. For example, the split sheath cartridge heater may include two generally semi-circular heater elements (or one element folded back over itself) sized to be received in the sleeve. Upon heating, the elements expand to force good thermal contact with the sleeve, thus promoting efficient heat transfer.
In another variation of the heater structure for use with the embodiments of the first aspect of the present invention, an impedance type heater unit is utilized. Generally, the impedance type heater unit includes at least a first conductive metallic element for producing heat. Further, in the impedance heater unit the heater system""s electrical interface is provided by way of a first electrical lead connected to a first point on the metallic element and a second electrical lead interconnected to a second point on the metallic element during operation of the heating system. These leads interface with the power source such that an electric current passes through the metallic element. One of the electrical leads is preferably disposed in an adjacent relationship with the metallic element along a conductive path between the first and second connection points to produce a magnetic flux within the metallic element such that the metallic element may itself function as a resistive type heating element.
The metallic element utilized with the impedance heating unit may generally incorporate any shape, so long as the metallic element is electrically conductive and has magnetic properties (e.g., steel, iron, or other ferromagnetic materials). For example, the metallic element may be similar to the sleeve member discussed above wherein each end of a ferromagnetic sleeve member is interconnected to the power source such that an electrical current travels through the sleeve and at least one lead is disposed adjacently to the sleeve""s surface between the first and second ends. Alternatively, the metallic element may be a metallic plate embedded within a concrete or other prefabricated railroad tie. Regardless of what metallic element is used, it is preferable that the electrical leads used to interconnect the metallic element to the power source are disposed beneath the element such that they are further isolated from the track environment (i.e., non-protruding).
In a second aspect of the present invention the system""s heater assembly has a heater structure that is integrally formed within a railroad structure located in the section of railroad to be heated. In this regard, the heater structure may utilize part of the railroad structure in the section of railroad to be heated to generate the heat required to keep that railway section free from snow and ice. Accordingly, where the heater structure is integrally formed within the railway structure there are substantially no heater elements protruding above the surface of the rail structure.
Various refinements exist of the elements noted in relation to the second aspect of the present invention. Further features may also be incorporated in the second aspect of the present invention as well. These refinements and features may exist individually or in any combination. In one embodiment of the second aspect of the present invention the heater structure is integrally formed within a metallic tie. In this regard, the metallic tie itself is utilized as an impedance heating system""s metallic element such that the heater structure is integrally formed as part of the railroad structure (e.g., a sidewall of the tie). Utilizing the metallic tie, an electrical current may be passed through a portion of the metallic tie such that an impedance heating circuit is created. As will be appreciated, this provides for a heater element (the tie itself) that may have a substantial thickness such that it is resistant to damage and is substantially immune from burnout as is common with some resistive type heater elements. The tie also provide increased heat transfer to the area to be heated (i.e., track rails and the area therebetween) since the heat is generated within the metallic tie""s wall there are no heat transfer losses as are typical with bolt on type electric heater elements. Additionally, metallic ties are generally hollow which provides an inside surface for interconnecting all the heating system""s components such that none of these components protrude into the track rail environment. In this regard, a heater may be conveniently bolted within the tie. Such a heater may also be utilized to effectively heat switch systems that incorporate certain elements, such as tie rods and the like, within the interior space of the hollow tie. It will be appreciated that such switching systems include other elements that are exposed to the external environment and may therefore benefit from heating. These systems can be effectively heated by the various heater embodiments described herein.
In another embodiment of the second aspect of the present invention, a heating system utilizes a heater structure integrally formed in the rail track itself for heating a section of railroad track. In this regard, the rail track is utilized as the metallic element for an impedance heating unit. A first electrical lead interconnects a first section of the rail track and a second electrical lead interconnects a second portion on the rail track such that an electrical current may flow through the rail. Preferably the rail track will include a recess in which one of the electrical leads may be disposed adjacent to the rail track such that that lead does not protrude above the rail surface. This recess may be located on the bottom of the rail track to provide an additional degree of protection for the electrical lead. In addition, both leads may interconnect the track rail on the bottom surface such that the impedance heating system has no elements protruding from into the rail track environment. As will be appreciated, this embodiment of the present invention provides a system where the heat is directly generated within and by the rail track. In this regard, there are no conductive or radiative heat transfer losses in providing heat to the track rail. Accordingly, the efficiency of the rail track heater is improved allowing for a section of a railway to be effectively heated using less power than is required with bolt on or contact heater element systems.
A further feature related to any embodiment of the first and second aspects of the present invention deals with avoiding signaling interference that may be caused by the electrical energy of the heating system. This is especially pertinent in the second aspect of the present invention where the track rail is utilized as an impedance heating element that carries an electrical current for heating purposes. As will be appreciated, it is common for railroad tracks to carry various communication signals to and from trains traveling thereon. These signals may include, among others, switching commands and direct communications between a train and a control center. By applying an electrical current through the rail or creating an electromagnetic field of sufficient strength near the rail, the communication signals carried by the railroad tracks may experience interference. In this regard, it is desirable to provide means for preventing the heating system from unduly interfering with the communication signals. Various alternatives exist to accomplish this task. For example, the communication signals may continue to use the track rail as a communication medium so long as the heating energy (i.e., current) or electromagnetic field is sufficiently different from the communication signals so as to be easily distinguishable. This may be accomplished using sufficiently different frequencies for the communication signals and heating currents and/or filtering means such that any undesirable signals may be distinguished/filtered out of the communication signals. Alternatively, some sort of parallel path may be used to route the communication signals around the section of the track being heated. That is, the communication signals may avoid any interference that may be caused by the heating system by being routed around the heating system. Further, signals may utilize some other transmission medium. For example, the voice communication signals may be transmitted over the air and switching signals may utilize optical sensors, eddy current sensors and/or pressure transducers to detect the presence of a train. Accordingly these optical sensors and/or transducers may be hardwired to the track switch control, thereby eliminating the need for in track communications, etc. Regardless what means is utilized, what is important is that the communication signals are not unduly affected by the heating system.